Setting aside the many ethical and moral problems, supporting suicide as a solution is in effect elevating Jack’s disorder above his own worth as a human being. It’s giving power to his mental illness, and conceding defeat when there is still hope.
This is the exact opposite of what we do as therapists. People are not defined by their mental disorders. They are not powerless, they do have personal agency to live full, meaningful, value-driven lives amid depression, anxiety, or any other mental illness. None of these disorders precludes living a fulfilled, dignified life.
Furthermore, electing to take one’s own life while suffering from a mental disorder certainly presupposes that person is unfit to make rational decisions regarding his or her personal welfare, or at the very least about major life decisions, under which assisted suicide would definitely fall.